The present application is the National Phase of International Application PCT/CH2004/000393, which claims priority from European Application 03405483.3 filed Jun. 30, 2003.
The invention relates to a bus-based safety system of an elevator installation and a method for checking the safety system of an elevator installation.
Elevator installations comprise a safety circuit in which several safety elements, such as, for example safety contacts and safety switches, are arranged in a series connection. The contacts monitor, for example, whether a shaft door or the cage door is open. The elevator cage can be moved only when the safety circuit and thus all safety contacts integrated therein are closed. Some of the safety elements are actuated by the doors. Other safety contacts, such as, for example, an over-travel switch are actuated or triggered by the elevator cage.
The safety circuit is connected with the drive or the brake unit of an elevator installation in order to interrupt the travel operation if the safety circuit is opened.
Safety systems with safety circuits of this kind are subject to numerous disadvantages, which are briefly listed in the following on the basis of a few examples:                Every safety circuit has inherent problems; belonging to these are the length of the connections, the voltage drop in the safety circuit and the comparatively high cost of mounting.        The individual safety contacts are relatively susceptible to disturbance; unnecessary emergency stops of the elevator system can therefore happen.        The safety circuit does not permit a specific diagnosis; i.e., when the safety circuit is open it is only established that at least one safety contact is open.        A precautionary maintenance is not possible, since no indications about the state of the safety contacts of the safety circuit takes place. It is thus not possible to preventatively maintain the elevator installation and replace worn safety contacts in good time at a point when the elevator installation can be shut down without problems, be it within the scope of a periodic inspection, wherein, however, in many cases taking the elevator installation out of operation, which is not in itself necessary, is carried out.        
The availability of the installation can be restricted in an unnecessary manner, since the detection of an open safety contact always has the consequence of placing the elevator installation out of operation.
It was therefore proposed to equip elevator installations in the future with a safety bus system instead of with the mentioned safety circuit. The safety bus system typically comprises a control unit, a safety bus and one or more bus nodes.
A safety system with a safety bus is described in Application EP 01810903.3, which was filed on 18 Sep. 2001. The safety bus is used in order to enable a safe and reliable monitoring of the shaft doors of the lift installation.
In a further patent application EP 01810904.1, which was filed on 18 Sep. 2001, there is described a safety system with safety bus which allows an intelligent evaluation of the state of cage and shaft doors.
A safety system with safety bus comprises, in the case of some of the proposed embodiments, at least one bus node which can, for example, be connected with a safety element in order to interrogate the state thereof. Thus, information about the instantaneous state of the safety elements can be provided. In manner similar to conventional elevator installations with a safety circuit, a reaction can be triggered depending on the respective state of the safety element.
Such safety systems with a safety bus have to be constructed to be safe. Otherwise, for example, undefined states or erroneous interpretations can happen. In particular, the interrogation of the safety elements of the safety system by way of the safety bus must be absolutely safe and reliable.